1. Field of the Invention
The present invention relates to a photo-chemical remediation of Cu-CMP (Chemical Mechanical Polishing) waste streams, and more particularly to a remediation process that adds a photo-catalyst to waste streams in CMP processes to deposit copper ions, decompose organic pollutants via UV radiation and ultimately produce a clean waste stream.
2. Description of Related Art
Chemical Mechanical Polishing (CMP) has become the key planarization technology for the fabrication of ultra large-scale integration (ULSI) silicon devices that contain sub-quarter micron metal and dielectric lines.
In conventional CMP processes, aluminum is used as interconnecting material. Before the introduction of copper as the interconnecting material to replace aluminum, the CMP waste treatment was not a major issue. Silica and fluoride contaminants in the CMP system using aluminum are diluted with water from other facility processes and commonly routed to an acid waste neutralization system. After replacing the aluminum in the CMP system with copper, many new challenges are experienced in the treatment of post process waste streams. The Cu-CMP process is a major consumer of resources (slurry) and most of all is a producer of solid waste (pad) and waste containing effluent (spent slurry).
Common Cu-CMP process effluent contains a variety of organic and inorganic contaminants that originated from the slurry, and tool discharged and post-CMP cleaning processes. The fate and transportation of these pollutants depend on several factors, which include pH and redox-chemistry of the treatment system.
Organic materials commonly found in the CMP effluent include metal complexing agents, surfactants, stabilizers, and corrosion inhibiting agents whose solubility is highly dependent on the pH of the slurry. One example is the aromatic amine, benzotriazole (BTA) that is used as a corrosion inhibitor and copper removal control agent. BTA forms a water-soluble complex with copper being an acid salt at a low pH condition. As the pH is increased toward the alkaline regime, the soluble complex become insoluble and thus may increase the strain on the post process treatment. Dispersing agents, such as polyacrylic acid, remain water-soluble over a large pH range and thus the adjustment of the pH may not be an effective mechanism of waste removal. The coagulation of solids in the system may be an effective mechanism of removal but the addition of organic additives to the slurry may result in a system difficult to flocculate in post process treatment.
Inorganic materials commonly present in post-process effluent are insoluble materials from the slurry abrasive (ceria, alumina, silica) and have a concentration range of 50–500 ppm. The abrasive particles tend to be well suspended in the large volume of water present and are commonly in the oxidized forms. The presence of soluble inorganic materials is commonly a result of the oxidizer of choice such as hydroxylamine and hydrogen peroxide.
The major inorganic contaminants are the materials that are removed from the surface of the wafer, such as metals, metal oxides, and low coefficient dielectric materials. During the Cu-CMP process, approximately micron of Cu metal is removed from the surface of the wafer, which translates into about 0.28 g of Cu per metal layer for a 200 mm diameter wafer process. Along with the abraded materials are some inorganic and organic materials that must also be treated. Common processes will provide a means to treat each class of components separately in a multi-step treatment system. Therefore, conventional treatment system of Cu-CMP waste streams is complex and has multiple factors such as pH condition and redox-chemistry etc. which influence the efficiency of the treatment system.
The present invention has arisen to provide a remediation for Cu-CMP waste streams to overcome and obviate the drawbacks of the conventional treatment system.